Technology of shipboard two-way microwave time synchronization

For the high precision time synchronization demand of ships, advantages and disadvantages of the present time transfer methods are analyzed, the two-way microwave time transfer （TWMTT） method is adopted to resolve the time synchronization problem in the Naval Ship Formation. After expounding the principle and system composition of TWMTT method, the various factors influencing the synchronous precision are analyzed, such as time-interval measurement error, TWMTT equipment delay error, signal propagation error in air, and signal delay error caused by shipping. To improve the time synchronization precision, all the error sources above are deduced with mathematical measures to definite the critical one, and the signal processing measures such as Pseudo code spread spectrum time comparison signal generation technology, FFT fast acquisition technology and precise tracking technology are used into the modem which is the core equipment of the TWMTT. And, calibration method of TWMTT equipment delay are developed. Through theoretical a- nalysis and simulation verification, the precision of shipboard two-way microwave time synchroniza- tion can reach 1 ns.

Time synchronization and ranging under unknown positions and velocities

The process to achieve time synchronization and ranging for a network of mobile nodes is raising a concern among researchers, and hence a variety of joint time synchronization and ranging algorithms have been proposed in recent years. However, few of them handle the case of all-node motion under unknown positions and velocities. This study addresses the problem of determining ranging and time synchronization for a group of nodes moving within a local area. First, we examined several models of clock discrepancy and synchronous two-way ranging. Based upon these models, we present a solution for time synchronization with known positions and velocities. Next, we propose a functional model that jointly estimates the clock skew, clock offset, and time of flight in the absence of a priori knowledge for a pair of mobile nodes. Then, we extend this model to a network-wide time synchronization scheme by way of a global least square estimator. We also discuss the advantages and disadvantages of our model compared to the existing algorithms, and we provide some applicable scenarios as well. Finally, we show that the simulation results verify the validity of our analysis.

航天测量船高精度岸船对时技术

随着航天技术的飞速发展以及新型号航天发射任务对测控系统提出的新要求,采用新技术新方法提高航天测量船的岸船对时精度非常必要。重点介绍卫星双向时间比对技术的基本原理,分析岸船卫星双向时间比对中影响岸船对时精度的主要误差源及其精度,提出实现高精度岸船对时需注意的问题。

A Service-Oriented Architecture of Cyber-Physical System and Study on Two Key Issues

As the basis of designing and implementing a cyber-physical system (CPS), architecture research is very important but still at preliminary stage. Since CPS includes physical components, time and space constraints seriously challenge architecture study. In this paper, a service-oriented architecture of CPS was presented. Further, a two-way time synchronization algorithm for CPS service composition was put forward. And a formal method, for judging if actual CPS service meets space constraints, was suggested, which was based on space-π-calculus proposed. Finally, a case study was performed and CPS business process designed by the model and the proposed methods could run well. The application of research conclusion implies that it has rationality and feasibility.

Research on inter-satellite measurement technique in high dynamic environment

An improved measurement algorithm, based upon the theory of two-way time transfer （ TWTT）, is proposed to measure satellites with high speeds. The algorithm makes theoretical analyses and corresponding deductions on a relative motion model of two satellites, and eliminates the measurement error caused by the equipment delay when a satellite moves at a high speed. Theoretical analysis and simulation results demonstrate that in comparison with the conventional TWTT algorithm, the proposed algorithm can significantly enhance the measurement accuracy of the inter-satellite ranging and time synchronization, and the algorithm is more effective with the relative velocity between the satellites and transmitting delay becoming larger.

同步定时网络相关选源机制探讨

本文就现阶段同步定时网架构下,影响网络选源机制的相关因素及主、从时钟间验证机制进行分析,并适时提出一些解决方案,以便于将来网络规划及设备研制提供借鉴及参考。

On new measurement and communication techniques of GNSS inter-satellite links

This paper studies the key techniques of the measurement and communication system for inter-satellite links(ISLs) of global navigation satellite system.A fixed link topology is designed based on the analysis of inter-satellite geometric properties and spatial parameters of the standard Walker24/3/2 constellation.This design can achieve full network coverage with small num-ber of hops,significantly reduce the number of ISLs,and enhance the feasibility and reliability of the system.A new time-division duplex mode,as well as an integrated measurement and communication scheme,is proposed based on the de-signed topology.Furthermore,mathematical formulas,error models,and modification methods regarding two-way ranging and time synchronization algorithms using spread spectrum non-coherent data frame for this new system are comprehensively dis-cussed.Theoretical analysis and simulation studies demonstrate that our design,compared with current GPS systems,has higher ranging and time synchronization precision,improved measurement efficiency,and higher channel utilization ratio and data transmission rate.It has no restrictions of constellation configuration,making it suitable for both MEO and the future MEO/GEO hybrid constellations.The results in this paper can serve as strong technical support for the next generation of GNSS ISL.